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problems with rock candy crystals

Postby dshah73 » Wed Mar 04, 2015 7:43 am

Good Morning,
I've been assisting my 2nd grade daughter with her science fair project--to compare the rate of growth between seeded and non-seeded rock crystals. We started the experiment several days ago--followed the recipe/instructions on sciencebuddies.org to the line. But, not a single crystal or hint of a crystal is forming along the string. We have seen plenty of crystals on the surface though. We've tried breaking those up to give the saturated solution below more air to crystallize as well as used a fan to help circulate the air near the jars, to also facilitate evaporation. Nothing seems to be working.

Last night, we tried to do a modified version of this experiment that allows for crystals to grow quicker: https://www.youtube.com/watch?v=-OX095k ... 3479501757 and our glass/jar turned into a solid rock of sugar after about an hour. Is this a problem with how we cooled the jar? We had pre-heated the jar with boiling water and waited for the sugar syrup solution to cool a bit before we added it to the jar. I don't know what we are doing wrong. Seems like one of the easier experiments to do and we just can't get anything going!

Please help!
Thank you.

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Re: problems with rock candy crystals

Postby alexagiammarino » Tue Mar 10, 2015 8:16 pm

Hi! It seems like you did the experiment right the first time. It is normal to get a thin layer of crystals on the top layer of your sugar solution in the jar. On the seventh day you want to gently break those crystals enough so when you pull out the string, there is no disruption to the crystals on the string. If you see absolutely no crystals on the string you may not have heated the jar enough before pouring in the solution. Also, you don't want to put a fan or anything like that near the jars. Although it seems like it would speed up evaporation, it actually is disrupting the temperature and growth of the crystals. Try to keep the jars on a counter or shelf away from fans and sunlight. The evaporation will occur spontaneously. Also make sure you are adding the exact right amount of sugar to the solution. Differences in dilutions can cause a shift in crystal growth. If all of this is done and the experiment still doesn't work, my only other suggestion would be to use a wooden skewer or chopstick instead of string. Growing crystals is a tedious and delicate thing to do. I did this experiment a bunch of times in a few of my classes and trust me its not as easy as they make it sound. It takes a while to do because the rate of evaporation has to be at a proper speed to allow for the formation of suitable crystals. Keep trying though! Im sure you'll get it! Good luck! :D

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Re: problems with rock candy crystals

Postby rk325 » Tue Jan 05, 2016 4:35 pm


We followed the instructions for growing crystals with seeded and non-seeded strings, but lots of crystals grew in the bottom of the jars, on the side walls of the jar and on top. The top layer we broke easily, but our string with the crystals it grew on it got glued on the bottom and sides of the jar so it was impossible to pull out the string from the jar without breaking the crystal structure. WE noticed formation of crystals in the bottom and the walls of the jar on the 2nd-3rd days. What can we do to avoid our grown rock candy glue in the bottle?

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Re: problems with rock candy crystals

Postby tdaly » Fri Jan 15, 2016 10:36 am

Hi rk325,

Crystal growing experiments can be really finicky. Like you said in your first point, growing crystals seems like a relatively easy experiment. But, after working with a lot of people doing these types of projects, there are many different things that can cause hiccups in the experiments. So, know that a lot of people run into troubles of one kind or another when doing a crystal growing experiment.

It sounds like you are at least having success growing crystals on the string now - which is wonderful! One way to prevent crystals from "gluing" the string to the sides and bottom of the jar would be to (a) use a shorter string and (b) use a wider jar. You could also try using a glass mixing bowl, so long as the string doesn't go more than about halfway to the bottom of the bowl.

Keep in mind that your daughter's project is still a success, even if the crystals aren't growing in the places you want them to. You made a hypothesis, followed a procedure to do an experiment, and made observations. As long as you interpret those observations in a way that is consistent with your observations, the project is a success.
All the best,

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